Ground state of double beta decaying nuclei

Recent results concerning the ground state of proton neutron systems are reviewed. A schematic Hamiltonian is treated by a time dependent formalism. New harmonic motions and static properties are pointed out. Applications to single beta and 2nubetabeta decays are given. Also the isospin symmetry restoration is discussed. It is shown that inclusion of scattering terms in the expression of the pnQRPA phonon operator enables to account for the isospin wobbling motion. Predictions obtained in the new approaches are compared with the corresponding exact results.